Abstract: Based on the present fracture toughness test methods for metallic materials,the fracture toughness K_C of A7N01P-T5 aluminum alloy was first tested according to the national standard GB4161-2007 and the corresponded analysis was also carried out. The new analytical formula of fracture toughness, which was related to the plate thickness,was proposed based on the energy theory and linear elastic mechanics. CTOD test was conducted to verify the accuracy of the new formula. The results show that the analytical formula could be used for various plate thicknesses,and also it could provide theoretical guidance for testing fracture toughness of other metallic materials. This work could not only save manpower and material resources,but significantly reduce the calculation cycle of remaining life of structures in structural integrity assessment of welded structures. Meanwhile,it also provides general methods and reference rules for obtaining the K_C of other metallic materials.